Some prior art communication systems utilize multibutton station sets having general call appearance (CA) buttons for initiating a first type of call (one using shared facilities) and dedicated CA buttons for initiating a second type of call (one associated with a specific facility). In some of these systems, the number of CA buttons at the station set is exceeded by the number of extensions served by the communication system. To enable a user at a station set to access all of these CO lines, the CA buttons are dynamically assigned on a call basis. No one button is associated with a given CO line. Instead, the CA buttona are assigned in some predetermined order as calls are originated or received.
In these systems, each dedicated CA button is usually assigned to a particular one of a plurality of second call types. These dedicated CA buttons are used for both originating and terminating the second type of telephone call. When originating these second type of telephone calls, the dedicated CA buttons are used, for example, to specify the dialplan to be used (automatic intercom, etc.), simplify billing procedures (secondary extensions), and access specific facilities (personal central office lines). When terminating telephone calls, the dedicated CA buttons are used to indicate the status of a specific facility, or to indicate the party that the caller was trying to reach (secondary extensions, coverage, etc.)
In some systems having dynamically assigned CA buttons and dedicated CA buttons, certain call features, such as conferencing, had to be implemented differently depending on whether the call feature was initiated from a dynamically assigned CA button or a dedicated CA button. This often resulted in the conferenced dedicated CA button remaining tied up if a conference call was ended by a CO party dropping off an intercom connection. Thus, in the prior art when call conferencing and call transfer features were activated, either certain sequences of operations had to be prohibited or the dedicated CA buttons were forced into ambiguous states resulting in user confusion.
Accordingly, it is an objective of our invention to provide a communication system permitting each station set user consistent access to the various call types. It is a further objective to permit users to initiate these call types using a station set having only general CA buttons.